Removal by means of pebbles of asphalt deposited during propane fractionation of lubricating oils



Sept. 27, 1955 B. .1. MAYLAND 2,719,107

REMOVAL BY MEANS OF PEBBLES OF ASPHALT DEPOSITED DURING PROPANE FRACTIONATION OF LUBRICATING OILS Filed July 3, 1950 7] PRODUCT OIL 32 PROPANE PHENOL STRIPPING ZONE EXTRACT OIL PROPANE FLASH ZONE EXTRACTION ZONE 6 l6 PROPANE INVENTOR. B.J. MAYLAND ATTORNEYS United States Patent REMOVAL BY MEANS OF PEBBLES OF ASPHALT DEPOSITED DURING PROPANE FRACTIONA- TION OF LUBRICATING OILS Bertrand J. Mayland, Bartlesville, Okla, assignor to Phillips Petroleum (Iompany, a corporation of Delaware Application July 3, 15 50, Serial No. 171,794

12 Claims. (Cl. 196-1446) This invention relates to propane fractionation of lubricating oil stocks. In one aspect, it relates to a method for the treatment of low asphalt-content lubricating oil stocks for the simultaneous separation of lubricating oil fractions and the removal of asphaltic material. In still a more specific aspect, it relates to a process for the separation and recovery of lubricating oil fractions from low asphalt-content crude lubricating oil stocks containing some resinous material by fractionation with propane wherein the asphaltic and resinous materials are precipitated and removed from the lubricating oil fractions.

The asphalt content of a crude oil may conveniently be defined as the per cent of residue from the vacuum distillation of a crude oil, said residue having a maximum A. S. T. M. 13243-36 penetration of 100 at 77 F. For

Oklahoma City crude oils this asphaltic residue constitutes about 2 per cent by weight of the crude oil.

By the term low asphalt-content crude oil, I mean crude oils containing a maximum of about 5 per cent asphalt by weight as determined by the above-mentioned A. S. T. M. method. Such a low asphalt-content crude oil may be distinguished from asphaltic crude oils containing more asphalt, such as California crudes which contain from 12 per cent to 65 per cent asphalt, andv from Wyoming and Arkansas crude oils which contain about 30 per cent asphalt.

Deasphalting petroleum oils and more particularly reduced crude oils from which distillate lubricating oil fractions have been removed is old in the art. Such operations are usually carried out at temperatures between about 70 and 140 F. to take advantage of the precipitating action of propane on the heavy asphaltic constituents of the oil. It has also been recognized for many years that a fractionating effect can be obtained with propaneoil mixtures at temperatures ranging from about 140 F.

up to the critical temperature of propane or higher. Utilizing the unique properties of liquid propane whereby increasing temperatures result in progressive rejection of hydrocarbons in such a manner that the higher molecular weight components and the more aromatic and naphthenic components are rejected first and the lighter components and more paraffinic hydrocarbon last, a combination of low temperature distillation and solvent extraction is achieved. However, due to the difficulties involved in working at high pressures and in close proximity to the critical temperature of propane, commercial exploitation was unknown until quite recently.

It has been found, however, that some low-asphalt content reduced crude lubricating oils may be fractionated continuously by liquid propane under high pressure and at a relatively high temperature, while other such crude oil stocks can be fractionated only for very short periods of time. In this latter case, it has been found that the fractionating equipment became plugged with a deposit of asphaltic material. This asphaltic material has apparently been precipitated from the oil upon contact with the high temperature propane. It should be mentioned 2,719,107 Patented Sept. 27, 19155 that the oils in question were low asphalt content oils and did not differ significantly from each other in total asphalt content, as conventionally determined. Why some oils caused plugging trouble and others did not is not clearly understood. When operating in this manner for the production of SAE 30 to 50 grades of lubricating oils, deposits within the fractionating column often occur in from 30 to 60 hours of continuous operation to such an extent that the column becomes completely plugged against the flow of materials. At the end of this short operating period, operation must be suspended in order to remove the asphalt plug. The deposition usually takes place at andbelow the entry point of the charge oil.

An object of my invention is to devise a process in which a low-asphalt content reduced crude lubricating oil stock is continuously fractionated for the separation and recovery of lubricating oil fractions.

Another object of my invention is to devise a process for the separation and removal of asphaltic and resinous materials from crude oil stocks containing these materials and the simultaneous separation of the lubricating oil fractions.

Still another object of my invention is to devise a process in which precipitated asphaltic and resinous materials may be removed from a propane lubricating oil fractionation process without precipitation of the asphaltic and resinous material in such a manner as to plug the treatpane-to-oil volume ratio of about 7:1 with temperatures ranging from about 195 F. at the top to about F. at the bottom of the tower, an SAE 40 oil was continuously separated in the overhead product. On the other hand, when a very similar Mid-Continent reduced crude lubricating oil stock was charged to the process under the same operating conditions. a similar fraction of lubricating oil was initially obtained, but the column rapidly filled with a hard asphaltic material in the stripping section thereby making continuous operation impossible. In this second case, a third phase, that is, a semi-fluid asphaltic phase was apparently produced along with a propane-rich light oil fraction and an oil-rich solution of propane in heavy oil. Upon contacting the charge oil with liquid propane, this third phase when first formed was sufficiently fluid to flow nearly to the bottom of the column before the ascending propane had washed it sufficiently to cause it to set to a hard cake. tinued operation, this cake builds up in the column until complete closure of the column occurs. Why one low-asphalt content oil should deposit its asphalt while another does not when the two oils contain similar amounts of asphalt is not definitely known.

In a study of three well-known Mid-Continent crude oils which have long been recognized as excellent sources of lubricating oil stocks, hard deposits were formed when treating two of these stocks with liquid propane while the third was fractionated with propane continuously and without difiiculty. It has also been found that some West Texas low-asphalt content reduced crude oils can be continuously fractionated with propane while others cannot. It is, therefore, realized that conventional pro- Upon conpane fractionation cannot be universally applied to all so-called low-asphalt content reduced lubricating oil stocks.

In my improved process, I use a vertically disposed elongated separation zone provided with bafi les or other suitable mixing devices into which is introduced a stream of solid particulate material. The particulate material is preferably spherical-shaped, although irregular shapes may be used and has a diameter of from about to 1 /2 inches. Hereinafter, this flowable particulate material will be called pebbles. The pebbles may be formed from refractory material, such as mullite, alumina, silicon carbide, or they may be metallic in nature, as for example, iron, steel, or even aluminum.

In the drawing the figure represents diagrammatically, partly in section and partly in elevation, one form of apparatus in which the process of my invention may be practiced.

Referring now to the drawing, a reduced crude oil charge stock is introduced through a line 10, from a source not shown, through a feed line 11 into a vertically disposed treating column 14. This column 14 is provided with downward sloping baffles 15, as illustrated. In operation, a quantity of an oil-rich phase 61 is maintained in the lower portion of the column 14, and the remainder of the column is filled with liquid propane 62 containing some dissolved oil. This oil-rich phase and liquid propane meet at a common interface 50. Pebbles 18 are introduced at a rate from 0.2 to times the rate of reduced crude oil charged, by weight, into the propanerich phase at about a mid-point vertically or slightly below the mid-point of the propane phase. The oil feed stream is introduced into the column at a point somewhere near the pebble inlet point. However, under certain conditions, it may be desirable to introduce the feed oil into the column at a point somewhat below or somewhat above the pebble inlet point. Liquid propane is introduced into the column 14 through a feed line 16 at a point near the bottom of the column into the lower portion of the oil-rich phase 61. Sufiicient pressure is maintained in the column 14 so that the propane is in the liquid phase at all times.

A temperature of from about 190 to 210 F. is maintained in the uppermost part of the propane-rich phase in the column. A temperature gradient is maintained down the column with the feed point being maintained at a temperature of from about 155 to 185 F. The section below the feed point may be maintained at a constant temperature, or a temperature gradient may be maintained in this section of the column also with the bottom being maintained at a temperature from 145 to 175 F. The pebbles 18 and the oil feed from inlet pipe 11 are introduced into the column at a temperature of the contents of the column at their points of introduction.

The oil feed from inlet pipe 11 upon entering the column 14 contacts the propane-rich phase 62 and asphaltic material upon precipitation becomes attached to the surface of the pebbles 18. Any asphalt precipitated as a third phase when not adjacent a pebble becomes attached to a pebble by the time the asphaltic material reaches the interface 50 between the two liquid phases. The oilrich phase 61 is comprised of oily material of heavier SAE grade than the oil taken overhead with the propane. Any precipitated asphalt which might reach the interface 50 without having become attached to a pebble will enter the oil-rich phase 61 and in this phase further opportunity is present for an asphalt particle to become attached to a downward moving pebble. The propane introduced into the oil-rich phase through line 16 acts as a stripping agent and strips or dissolves propane-soluble oils from the oil-rich phase. While in the oil-rich phase, the propane with dissolved oils is a separate liquid phase. This propane phase is obviously lighter than the oil phase 61, and the propane rises as droplets toward the interface 50. Upon reaching the interface 50, the propane droplets become continuous with the propane phase 62, and the propane phase 62 rises or flows upward in the tower according to the rate of propane feed introduction through line 16. The temperature of the propane feed entering the column through line 16 is the same as the temperature of the oil rich-phase 61. Sulficient propane is added through line 16 to maintain a propane-to-charge oil ratio from 4 or 5:1 to 14:1 by volume. Makeup propane may also be introduced into the system through pipes 76 and 16 as needed, from a source not shown.

In the upper section of the column 14, that is, above the oil feed and the pebble inlet points, a precipitating or refluxing action takes place. Since oily materials are less soluble in propane at higher temperatures than at lower temperatures, maintaining the top of the column at the highest temperature in the propane phase causes precipitation of oily material. This oily material precipitated in the top of the column by the relatively high temperature propane settles downward due to specific gravity diiference between the precipitated oil and the propane phase. In settling downward, the oil droplets are washed by the up-flowing propane and this washing redissolves the lower molecular weight and less aromatic constituents from the down-flowing droplets. By maintaining a top temperature between about 190 and 210 F. and a pressure in the range of 600 to 700 p. s. i., the overhead oil when freed from propane is of SAE 30 to grade.

Oil-rich phase accumulating in the bottom of the contacting vessel 14 and pebbles with their coating of asphaltic material are removed from the bottom of the column through a conduit 19.

At the lower end of this conduit 19 the pebbles and asphalt are picked up by a bucket conveyor 20 which consists of buckets 22 attached to a belt 21. The bucket conveyor is operated by two pulleys 23 and 24. As illustrated in the drawing, the bucket elevator apparatus in this embodiment operates in a clockwise direction. The pebbles with their adhering asphalt are elevated in this conveyor, and in the lower portion of the elevator zone 20 is maintained a volume of an aromatic oil or such an oil as will dissolve the asphalt from the surface of the pebbles. The aromatic oil as a solvent for the asphalt is introduced into the conveyor apparatus through an inlet pipe 25. The temperature of this solvent is preferably maintained at a value somewhat lower than the operating temperature maintained in column 14. A satisfactory range of temperatures in the solvent phase in the elevator zone is between the limits of about and F. The aromatic oil introduced through pipe 25 is introduced at approximately the temperature maintained in the body of this solvent in the elevator. The solvent is preferably introduced through a spray nozzle 51 so that fresh aromatic oil will wash the upward rising pebbles in the conveyor after they have been removed from the body of solvent. The upper surface of the aromatic solvent oil in the conveyor apparatus is identified by reference numeral 26. The level of this liquid surface may be maintained at about the point illustrated in the drawing or may be even higher than this point, or lower, as found desirable. If the level 26 of this aromatic oil is maintained at a point higher than the inlet point of the solvent, the pebbles will not be washed with completely fresh solvent. It is preferable to maintain the level 26 at some distance below the solvent inlet point so that the pebbles will be washed with fresh solvent for more nearly complete removal of asphalt.

Makeup aromatic oil is introduced into the system through pipe 25, as needed, from a source, not shown.

The pebbles from the top of the elevator are discharged through a sloping conduit 27 into a propane washing zone 28. In this zone the pebbles are elevated by a bucket elevator 29 traveling around pulleys 30 and 31 in a clockwise direction. Liquid propane flowing through pipe 32 from a source, not shown, is sprayed onto the traveling pebbles through a spray nozzle 33. Whether or not liquid propane adheres to the pebbles is immaterial since the upper phase in the main contacting column 14 is a propane-rich phase. The small amount of propane so added does not adversely alter the propane-to-oil ratio in the column. From the top of the conveyor 29 the pebbles flow through a conduit 35 for introduction into the main treating column. The volumes of the main treating column 14, of conduit 19, of the elevator 20, of the conduit 27, of the wash zone 28, and of conduit 35 are all inter-connected so that this entire treating system may be maintained under approximately a common pressure. This treating system is operated under a pressure such that the required processing pressure is main tained in the propane column. Usually, pressures between about 600 and 700 pounds per square inch are utilized in the present process. Since the space above the liquid surface 26 in the elevator zone is a vapor space and that vapor space continues through conduit 27, propane washer 28 and conduit down to the liquid surface indicated by reference numeral 49, this surface 49 is a gas-liquid interface between the liquid propanerich upper phase from column 14 and the vapor phase. The pressures on surface 49 and surface 26 are the same. In order to maintain the upper portion of the elevator, propane Washer and conduit 35 under vapor phase conditions at all times, gas under pressure is introduced through line 48. Such a gas as hydrogen, nitrogen, methane, or even ethane or mixtures of these may be the gas used for pressure maintenance. Gases having higher vapor pressures than propane must be used so that a vapor phase can be maintained.

A mixture of aromatic oil and asphalt in solution in the lower portion of the elevator zone 20 and the oilrich phase containing some dissolved propane passing through conduit 19 are removed from the lower portion of the elevator zone through line 52. This material may be passed to a recovery unit for reclaiming of the aromatic oil and propane for reuse in the process. This aromatic oil and propane may be recovered in a recovery zone 63 which may be a distillation zone in which the propane is removed overhead, the aromatic oil as a side stream and the asphalt and heavy oil are a bottom product. The propane separated is removed through line 75 and may be recycled. The aromatic oil and vapors thereof are passed through line 74 to a condenser 64 for condensation and the condensate run into a run tank 65. From this run tank 65 the aromatic oil may be removed through line 66 for recycling to the process. Makeup aromatic oil from a source, not shown, is introduced into the system through line 67 as needed. The asphalt and heavy oil from the bottom of the recovery zone 63 may be passed to storage or subsequent processing or use, as desired, through line 68.

The propane phase containing dissolved oil is removed through an overhead line 17 from the tower 14 and is passed to a propane flash zone 36 in which propane is separated from its dissolved oil content. The flashed propane is removed from this zone 36 through pipe 37 and is condensed in condenser 69 and subsequently added to the charge propane entering the column 14 through line 16.

The oily material recovered from the propane phase in the flash zone 36 is removed from the zone through line 38 and is passed into a solvent extraction zone 39. In this solvent extraction zone 39 such an extraction solvent as phenol is used as an extractant for removal of the less paratfinic constituents from the oil. Accordingly, in such an operation, phenol enters line 41) from a source, not shown, and is introduced into the upper portion of the extraction zone 39. The extract phase is removed from the bottom of the extraction zone through line 42 and is conducted to a stripping zone 43 in which the phenol is stripped or distilled from the extract oil. This stripping zone 43 may be equipped with reflux producing coils and with reboiler coils, not shown. The

vaporous phenol removed from the top of the stripping zone 43 is passed through conduit 44, is condensed in condenser and the liquid phenol is subsequently passed through conduits 44 and 40 for reintroduction into the extraction Zone 39. The stripping zone bottoms comprising the extract oil is removed from the stripper through line 45 and is passed to such disposal or subsequent use as desired.

Under some conditions this extract oil may be sufficiently aromatic in nature as to be a good solvent for asphalt. If such is the case, this extract oil may then be passed through pipe 46 into pipe 25 for use in the elevator zone 20 as the solvent for removal of asphalt from the pebbles.

The extract phase from the bottom of the extraction zone 39 may be suitable as an asphalt solvent. When such is the case, all or a portion of the extract phase passing through line 42 may be passed through line 47 into line 4-6 and thence into pipe 25 for introduction into the bucket conveyor apparatus 20 for dissolving the asphalt.

When extract phase containing extraction solvent is used as the solvent for asphalt, this extraction solvent will then be removed from the conveyor zone 20 with the asphalt and oil-rich phase through line 52. This extraction solvent will then be recovered through line 74 from recovery zone 63 and it will accumulate in the tank 65. The solvent is then withdrawn from tank 65 and is passed through lines 66 and 71 and thence through pipe 40 to be added for recycling as extraction solvent into the top of the extraction zone 39. The extract oil will ordinarily pass from the recovery zone 63 through line 68 with the asphalt.

Raffinate oil containing a small quantity of extraction solvent is removed from the extraction zone through the pipe 41. The small amount of solvent carried in this raffinate phase may be recovered therefrom by distilla tion for recycling in the process. The recovered raffinate oil free from solvent is then ready for storage or use, as desired.

A bleed pipe 53 is provided in the upper gas portion of the bucket conveyor zone 20 for the continuous bleed ing of some gas. Under such conditions, pressure may be maintained more nearly constant in this propane systern.

The propane washings accumulating in the bottom of the washer zone 28 contain some aromatic oil solvent and/0r asphalt, and these washings are removed through a line 34. Recovery of the propane from the small amount of asphalt and/or aromatic oil may be in a flashing operation, which operation is understood by those skilled in the art.

If it is desired that the oil feed to the main propane column 14 be introduced at a point some further up the column, inlet pipe 12 is provided; while if it is decided to introduce the feed at a lower point, a pipe 13 is provided.

Included in the term pebbles is intended to be such materials as coal or coke. Solid particles of coal or of coke may be introduced into the propane fractionator for removal of the asphalt. When coal or coke is used, the general operation of the propane fractionator 14 is about the same as when refractory or metallic pebbles are used. One point of difference, however, is that the coal or coke has not as high a specific gravity as the other types of pebbles, and the settling down of the coal or coke will not be as rapid. The coal or coke containing a layer of asphalt may, if desired, be exposed to the solvent action of the aromatic solvent oil and the pebbles reclaimed for recycling to the process. The coal or coke and asphalt may, however, if desired, be briquetted for the production of solid fuel, and in such an operation the aromatic solvent oil will not be needed and no recycling of pebbles will be necessary. Only new coal or coke as pebbles will then be introducedinto the main fractionation tower.

Other aromatic oils, such as benzene, toluene, or the xylenes, may be used for removing the asphalt from the pebbles. Whatever aromatic oil is used as solvent preferably has a boiling point difiering sulficiently from that of the asphalt and from the oil-rich phase from the bottom of the contractor 14 as to be easily separable by fractionation.

The liquid-liquid interface 50 in the lower portion of the main fractionator 14 may be maintained constant by the use of a float controller apparatus, diagrammatically illustrated and identified by reference numeral 72. The level of the interface 50 may be controlled or maintained at a desired point in the column by control of the removal of the propane-rich phase through line 17. If it is desired, a similar liquid level control apparatus 73 may be installed in the conveyor zone 20 for maintenance of the level of the aromatic oil in this zone. This float controller apparatus may operate a motor valve in outlet 52 as illustrated.

Most of the control apparatus necessary for the smooth and continuous operation of such a system has not been shown, for purposes of simplicity. The installation and use of such equipment are well understood by those skilied in the art. Such equipment, not shown herein, includes such as pumps, valves, temperature and pressure recording and controlling apparatus and the like.

Example A low-asphalt content Mid-Continent crude lubricating oil fraction is vacuum fractionated to separate SAE and oils. The bottoms from this fractionation are processed in the apparatus of this invention with a top temperature of 195 F., a feed temperature of 175 F, and a bottom temperature of 165 F. The column pressure is 640 p. s. i. and a propane-oil ratio of 8:1 is used. The column shows no signs of plugging after 300 hours operation.

When this same oil is processed in a conventional propane column, the column plugs after a period of about 60 hours operation.

A toluene concentrate containing about 60 per cent toluene and obtained from the effluent of a hydroforming unit is used to remove the asphaltic deposit from the pebbles.

The above described flow diagram and operational conditions are given for illustrative purposes and should not be regarded as limiting the invention, the scope of which is set forth in the following claims.

Having described my invention, I claim:

1. In a process for the propane fractionation of lubricating oil constituents from low asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic material precipitates upon initial contact of the oil stock with the propane and adheres to and plugs the fractionation apparatus in the region adjacent and below the raw feed entry point, a method for continuously carrying out this fractionation operation without plugging said apparatus comprising maintaining a body of a liquid propane-rich phase in a first contacting zone, maintaining a body of an oil-rich phase below said body of propane-rich phase in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil-rich phase, introducing a stream of said lubricating oil stock into said body of propane-rich phase, introducing a stream of solid pebbles into said body of propane-rich phase, maintaining the top of said body of propane-rich phase at a higher temperature than that of said oil-rich phase, removing propanerich phase from the top of said zone, passing pebbles with adhering semi-solid to solid asphalt and oil-rich phase from the bottom of said zone to a second treating zone, Withdrawing oil-rich phase containing aromatic oil and a minor amount of propane in solution from the lower portion of said second zone, elevating pebbles with adboring semi-solid to solid asphalt in said second zone,

introducing an aromatic oil into said second zone at an intermediate level, removing Washed pebbles from the top of said second zone, introducing said washed pebbles into a third zone, introducing liquid propane into said third zone and therein further washing said pebbles with said propane, removing said further washed pebbles and introducing same into said first zone as said stream of solid pebbles, separating the oil-rich phase containing aromatic oil and propane into a propane fraction, an aromatic oil fraction and an asphaltic and heavy oil fraction, removing the latter fraction as one product of the process, and returning the aromatic oil fraction and the propane fraction to the process.

2. In the process of claim 1, maintaining the top of the first zone at a temperature between 190 and 210 F., the temperature at the bottom thereof at to F., the ratio of propane to the oil feed introduced into the first zone between the limits of 4:1 to 14:1 at a pressure greater than the vapor pressure of propane at the highest temperature of the first zone, and the rate of pebble introduction into said first zone being between 0.2 to 10 times the rate of reduced crude oil charged, by weight, to the first zone.

3. 1n the process of claim 1 wherein the aromatic oil is benzene.

4. In the process of claim 1 wherein the aromatic oil is a toluene concentrate.

5. In the process of claim 1 wherein the aromatic oil is a solvent extract high in aromatic hydrocarbon content.

6. In a process for the propane fractionation of lubricating oil constituents from low asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic material precipitates upon initial contact of the oil stock with the propane and adheres to and plugs the fractionation apparatus in the region adjacent and below the raw feed entry point, a method for continuously carrying out this fractionation operation without plugging said apparatus comprising maintaining a body of a liquid propane-rich phase in a first contacting zone, maintaining a body of an oil-rich phase below said body of propane-rich phase in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil-rich phase, introducing a stream of said lubricating oil stock into said body of propane-rich phase, introducing a stream of solid pebbles into said body of propane-rich phase at a level about midway vertically of said propane-rich phase, maintaining the top of said body of propane-rich phase at a temperature between the limits of to 210 F., and the oilrich phase at a temperature between 145 and 175 F. with a gradient throughout said zone and the top thereof always being at the higher temperature, removing propane-rich phase from the top of said zone, removing solid pebbles with adhering semi-solid to solid asphalt with oilrich phase from the bottom of said zone, separating the pebbles with said adhering asphalt from the oil-rich phase, maintaining a body of an aromatic oil-rich phase in a second zone, introducing a stream of said aromatic oil into the top of said aromatic oil-rich phase in said second zone, introducing the separated pebbles with said adhering asphalt into said body of aromatic oil-rich phase, removing pebbles from said body of aromatic oil-rich phase, introducing the removed pebbles as the first mentioned stream of solid pebbles into the body of propane-rich phase in said first zone, and removing a mixture of aromatic oil, dissolved semi-solid to solid asphalt separated from said pebbles, and oil-rich phase from the second zone.

7. In the process of claim 6 wherein the aromatic oil is a solvent extract high in aromatic content.

8. In the process of claim 6 wherein the aromatic oil is benzene.

9. In the process of claim 6 washing the solid pebbles removed from the body of aromatic-rich phase with liquid propane priorto introduction of the pebbles as said stream of solid pebbles into said body of propanerich phase in said first zone. 7

10. In the process of claim 6 wherein the rate of flow of solid pebbles through the first zone is from .2 to 10 times the rate of reduced crude oil charged to said first zone by weight.

11. In the process of claim 6 wherein the aromatic oil is a toluene concentrate.

12. In a process for the propane fractionation of lubricating oil constituents from low asphalt-content reduced crude lubricating oil stocks with liquid propane wherein solid asphaltic material precipitates upon initial contact of the oil stock with the propane and adheres to and plugs the fractionation apparatus in the region adjacent and below the raw feed entry point, a method for continuously carrying out this fractionation operation without plugging said apparatus comprising maintaining a body of a liquid propane-rich phase in a first contacting zone, maintaining a body of an oil-rich phase below said body of propane-rich phase in said zone, said bodies meeting at a common interface, introducing a stream of liquid propane into said body of oil-rich phase, introducing a stream of said lubricating oil stock into said body of propane-rich phase, introducing a stream of solid pebbles into said propane-rich phase, maintaining the top of said body of propane-rich phase at a temperature between the limits of 190 to 210 F., and the oil-rich phase at a temperature between 145 and 175 F. with a gradient throughout said zone and the top thereof always being at the higher temperature, removing propane-rich phase from the top of said zone, removing solid pebbles with adhering semisolid to solid asphalt with oil-rich phase from the bottom of said zone, separating the pebbles with said adhering asphalt from the oil-rich phase, maintaining a body of an aromatic oil-rich phase in a second zone, introducing a stream of said aromatic oil into the top of said aromatic oil-rich phase in said second zone, introducing the separated pebbles with said adhering asphalt into said body of aromatic oil-rich phase, removing pebbles from said body of aromatic oil-rich phase, introducing the removed pebbles as the first mentioned stream of solid pebbles into the body of propane-rich phase in said first zone, and removing a mixture of aromatic oil, dissolved semi-solid to solid asphalt separated from said pebbles, and oil-rich phase from the second zone.

References Cited in the file of this patent UNITED STATES PATENTS 2,037,318 Fenske et al Apr. 14, 1936 2,079,886 Voorhees May 11, 1937 2,213,798 Anne Sept. 3, 1940 2,367,385 Weeks et al. Jan. 16, 1945 2,470,339 Claussen et al. May 17, 1949 2,558,809 Benedict July 3, 1951 2,603,587 Simms July 15, 1952 

1. IN A PROCESS FOR THE PROPANE FRACTIONATION OF LUBRICATING OIL CONSTITUENTS FROM LOW ASPHALT-CONTENT REDUCED CRUDE LUBRICATING OIL STOCK WITH LIQUID PROPANE WHEREIN SOLID ASPHALTIC MATERIAL PRECIPITATES UPON INITIAL CONTACT OF THE OIL STOCK WITH THE PROPANE AND ADHERES TO AND PLUGS THE FRACTIONATION APPARATUS IN THE REGION ADJACENT AND BELOW THE RAW FEED ENTRY POINT, A METHOD FOR CONTINUOUSLY CARRYING OUT THIS FRACTIONATION OPERATION WITHOUT PLUGGING SAID APPARATUS COMPRISING MAINTAINING A BODY OF A LIQUID PROPANE-RICH PHASE IN A FIRST CONTACTING ZONE, MAINTAINING A BODY OF AN OIL-RICH PHASE BELOW SAID BODY OF PROPANE-RICH PHASE IN SAID ZONE, SAID BODIES MEETING AT A COMMON INTERFACE, INTRODUCING A STREAM OF LIQUID PROPANE INTO SAID BODY OF OIL-RICH PHASE, INTRODUCING A STREAM OF SAID LUBRICATING OIL STOCK INTO SAID BODY OF PROPANE-RICH PHASE, INTRODUCING A STREAM OF SOLID PEBBLES INTO SAID BODY OF PROPANE-RICH PHASE, MAINTAINING THE TOP OF SAID BODY OF PROPANE-RICH PHASE, AT A HIGHER TEMPERATURE THAN THAT OF SAID OIL-RICH PHASE, REMOVING PROPANERICH PHASE FROM THE TOP OF SAID ZONE, PASSING PEBBLES WITH ADHERING SEMI-SOLID TO SOLID ASPHALT AND OIL-RICH PHASE FROM THE BOTTOM OF SAID ZONE TO A SECOND TREATING ZONE, WITHDRAWING OIL-RICH PHASE CONTAINIG AROMATIC OIL AND A MINOR AMOUNT OF PROPANE IN SOLUTION FROM THE LOWER PORTION OF SAID SECOND ZONE, ELEVATING PEBBLES WITH ADHERING SEMI-SOLID TO SOLID ASPHALT IN SAID SECOND ZONE, INTRODUCING AN AROMATIC OIL INTO SAID SECOND ZONE, INTERMEDIATE LEVEL, REMOVING WASHED PEBBLES FROM THE TOP OF SAID SECOND ZONE, INTRODUCING SAID WASHED PEBBLES INTO A THIRD ZONE, INTRODUCING LIQUID PROPANE INTO SAID THIRD ZONE AND THEREIN FURTHER WASHING SAID PEBBLES WITH SAID PROPANE, REMOVING SAID FURTHER WASHING PEBBLES AND INTRODUCING SAME INTO SAID FIRST ZONE AS SAID STREAM OF SOLID PEBBLES, SEPARATING THE OIL-RICH PHASE CONTAINING AROMATIC OIL AND PROPANE INTO A PROPANE FRACTION, AN AROMATIC OIL FRACTION AND AN ASPHALTIC AND HEAVY OIL FRACTION, REMOVING THE LATTER FRACTION AS ONE PRODUCT OF THE PROCESS, AND RETURNING THE AROMATIC OIL FRACTION AND THE PROPANE FRACTION TO THE PROCESS. 